In the related art, fluorine based polymers including polyvinylidene fluoride (PVDF) having superior electrochemical stability and chemical resistance have been used as electrode binders of nonaqueous electrolyte secondary batteries. Electrode binders play a role in holding active materials in a current collector and are required to have adhesion to a metal foil as well as binding capacity between active materials. Generally, PVDF, and the like has poor adhesion to metal, and depending on the active materials used, higher binding properties between active materials are desired.
Consequently, in order to improve these capacities as a binder, methods for copolymerizing vinylidene fluoride, and the like with other monomers have been developed.
Patent Document 1 discloses a vinylidene fluoride based copolymer obtained by copolymerizing vinylidene fluoride with a certain kind of unsaturated carboxylic acid.
Patent Document 2 discloses a vinylidene fluoride based copolymer obtained by copolymerizing vinylidene fluoride with certain kinds of hydrophilic acrylic monomers.
Patent Document 3 discloses that olivine type lithium phosphate, a fluorine resin having a crosslinkable functional group, a crosslinking agent, and a cathode electrode mixture slurry containing an organic solvent are applied onto the surface of a current collector, then heated to improve the adhesion between the current collector and the olivine type lithium phosphate, with at least one selected from the group consisting of alkylamine, aromatic amine, lithium hydroxide, and sodium carbonate used as the crosslinking agent.
Patent Document 4 discloses an electrode binder of a secondary battery using a nonaqueous electrolyte solution containing a fluorine-containing ethylenic polymer having a functional group obtained by copolymerizing, with respect to the total amount of fluorine-containing ethylenic monomers, 0.05 to 30 mol % of at least one fluorine-containing ethylenic monomer having a functional group having any one of: a hydroxyl group; a carboxyl group, a carboxylic salt, or a carboxy ester group; and an epoxy group.
Patent Document 5 discloses that an electrode binder obtained by thermally crosslinking polyvinylidene fluoride having a hydroxyl group with a polymer having an isocyanate group is used as an electrode binder.
Moreover, Patent Document 6 discloses, in a method for producing a battery electrode sheet by coating an electrode agent on a current collector, a method for producing a battery electrode sheet involving at least a pressing step after coating the electrode agent on the current collector and drying it, along with a step of subjecting it to heat treatment.